Preparation And Application Of SiO₂ And PMMA Monodisperse Colloidal Microspheres And Their Ordered Assemblies

In recent years,two-dimensional and three-dimensional colloidal crystals have received more and more attention due to their unique properties.Researchers have developed various types of self-assembly methods to prepare colloidal crystals,which were suitable for photonic crystals,sensors,inverse opal materials and many other fields.At present,the successful preparation of high-quality colloidal crystals has become one of the key issues affecting its further application.Based on the analysis of the current research status of colloidal microspheres and their ordered assemblies,this paper has carried out the following four aspects on the preparation and application of SiO₂ and PMMA monodisperse colloidal microspheres and their ordered assemblies.（1）The SiO₂ monodisperse colloidal microspheres were prepared by the modified St?ber method.The effects of TEOS concentration,water content,ammonia concentration and reaction temperature on the particle size and monodispersity of SiO₂ colloidal microspheres were investigated.Besides,PMMA monodisperse colloidal microspheres were prepared by soap-free emulsion polymerization.The effects of monomer concentration,initiator concentration and reaction temperature on the particle size and monodispersity of PMMA colloidal microspheres were investigated.The results show that the particle size of SiO₂ monodisperse colloidal microspheres increases with the concentration of TEOS and the concentration of ammonia.As the water to alcohol ratio changes from 0 to 0.45,the particle size of SiO₂ colloidal microspheres increases first and then decreases.When the water to alcohol ratio is 0.2,the microsphere size is the largest.As the temperature rises,the particle size of the SiO₂ colloidal microspheres gradually decreases.At the same time,with the increase of monomer concentration,the particle size of PMMA colloidal microspheres shows an increasing trend.However,with the increase of initiator concentration and reaction temperature,the particle size of PMMA colloidal microspheres shows a decreasing trend.（2）For the first time,capillary siphon self-assembly method was applied.In the process,monodisperse SiO₂ colloidal microspheres were dispersed in ethanol to obtain colloidal suspensions of different concentrations,and the capillary siphon was used to control the drop of colloidal suspension.Colloidal microspheres self-assembled on the vertical substrate with capillary force and electrostatic force,and finally the SiO₂ ordered assembly was obtained.Various experimental conditions were discussed,such as the falling speed of liquid surface,the volume fraction of SiO₂ colloidal microspheres and particle size.The results show that when the falling speed of liquid surface is 0.38μm/s and the volume fraction of SiO₂ colloidal microspheres is 3%,the colloidal crystal with the best order can be prepared.At the same time,the particle size of SiO₂ monodisperse colloidal microspheres is basically consistent with the position of Bragg diffraction peak.（3）PMMA ordered assemblies were prepared by air-water interface self-assembly method.During the process,monodisperse hydrophobic PMMA microspheres were dispersed into different disperant,and prepared into suspensions of different concentrations.PMMA multilayer colloidal crystals were obtained by using a original experimental device.Methanol,ethanol,n-propanol and isopropanol were used as dispersants,respectively,and the effects of suspension concentration,pH and microsphere size on assembly result were also investigated..The results show that the optimal dispersant is n-propanol.When the ratio of n-propanol to PMMA microsphere emulsion is 1:3 and the pH is between 4-5,colloidal crystals with the best quality can be prepared.In addition,the relationship between the PMMA monodisperse colloidal microsphere size and the Bragg diffraction peak position is basically in accordance with the Bragg diffraction equation.（4）The PMMA colloidal crystal obtained by self-assembly according to the above method was used as a template.The SiO₂ precursor sol was prepared by mixing TEOS,ethanol and dilute hydrochloric acid in a certain ratio.Then,the PMMA/SiO₂composite was obtained by filling the PMMA colloidal crystal template with SiO₂precursor sol.Finally,SiO₂ inverse opal material can be prepared by removing the PMMA template with acetone solvent.The structure was characterized by scanning electron microscopy（SEM）.It is found that the obtained inverse opal structure material has a three-dimensional ordered pore structure.